1995 Volume 44 Issue 10 Pages 543-549
In order to evaluate the corrosion rate of reinforcing steel (rebar) in coated concrete, the polarization resistance (Rp) of rebar was measured on the surface of concrete covered with and without various coatings by means of the coulostatic method. It was shown that Rp of rebar could accurately be measured on the bare surface of concrete by a combined sensor composed of reference and auxiliary electrodes and the values of Rp depended on the measuring time of decay curve of overpotential. Although the erroneous Rp values were obtained on the surfaces of epoxy and lacquer coatings, the normal values were measured in concrete under the coatings and on the epoxy primer paint with a low resistance. Based on comparison of decay curves, obtained on the coatings together with those measured under the coatings, it was revealed that residual voltage through the coating unavoidably measured by the combined sensor resulted in wrong Rp values. By separating a reference electrode from an auxiliary electrode, the decay curves being not affected by the residual voltage could be obtained and accurate Rp values of rebar could be evaluated even in the case of the coated concrete.